The present application claims priority under 35 U.S.C. 119 and 35 U.S.C. 365 to Korean Patent Application No. 10-2006-0128326 (filed on Dec. 15, 2006), which is hereby incorporated by reference in its entirety.
An image sensor may be a semiconductor device that may convert optical images into electric signals. An image sensor may be classified into horizontal and vertical image sensors.
A horizontal image sensor may be operated in such a manner that transistors may be formed on a semiconductor substrate corresponding to the number of pixels through a CMOS technology. The transistors may be switched such that an output signal may be detected.
Further, in the horizontal image sensor, a color filter may be formed on a pixel array, and the color filter may transmit a specific wavelength of light to the transistors. However, since the color filter may require three pixels to detect red, green and blue colors, the required area of a pixel needed to realize one color may become broader.
In contrast, a vertical image sensor may include photodiodes having various colors, which may be vertically formed on a plurality of epitaxial layers. Accordingly, various colors may be realized using a single pixel.
Gates may be formed in an upper layer of the vertical image sensor, and a diffusion area may be formed between the gates. A photoresist pattern may be used to perform two functions, including defining the diffusion area and selectively isolating ions implanted into the diffusion area.
The photoresist pattern should preferably have a small thickness, less than or equal to a reference value, to precisely define the diffusion area. However, the photoresist pattern should preferably have a large thickness to selectively isolate ions implanted into the diffusion area.
Therefore, a gate may be first formed using a first photoresist pattern, and a second photoresist pattern may be formed on the gate, thereby selectively opening the diffusion area.
However, since the dual photoresist patterns may contain a large amount of ions, they may be easily cured in the subsequent process. Since it may be difficult to remove the dual photoresist patterns through the cleaning process, the electrical characteristic and operation reliability of a device may be degraded.